In the production of window units, such as double-hung and casement-type window assemblies, it is common to use wood strips to form the frame members and the sash members around each glass panel unit. The exterior portions of the wood members are sometimes covered with a vinyl layer or cladding to provide weather protection for the wood members and to eliminate the need for periodic painting or staining of the members. For example, U.S. Pat. No. 3,340,665 discloses the use of formed plastics sheeting material over the exterior portions of the wood frame members. U.S. Pat. No. 3,662,494 discloses wood frame members covered by an extruded cladding of plastics covering material. The extruded material has integral ribs and flanges which project into grooves within the wood for securing the cladding to the frame members.
Similarly, U.S. Pat. No. 4,479,331 discloses a double hung window assembly with extruded vinyl cladding strips secured to the wood frame members as well as to the wood sash members. The vinyl cladding may be extruded as separate strips which are cut and attached to the wood members or components, as shown in the above U.S. Pats. No. 3,662,494 and No. 4,479,331, or the cladding may be applied by passing each wood member or component through an extrusion head which extrudes a layer of vinyl directly onto the component.